This article, Part I of a two-part series, discusses the incredible findings of Nathan Senner’s phD research on Hudsonian Godwits, which he is currently finishing up at the Cornell Lab of Ornithology.
Shorebirds have been in the birding news a lot recently as migratory routes are deciphered using amazing tracking devices called geolocators, which use measures of daylight hours to triangulate a bird’s location. The most famous of these stories is that of Bar-tailed Godwits and their 11,700km (7,000+ mile) non-stop trip from Alaska to New Zealand. But another godwit, one more familiar to North American birders, has an equally incredible story, one that is finally being deciphered by Nathan Senner, a phD candidate at the Cornell Lab of Ornithology.
Hudsonian Godwits are rare migrants in much of North America. This bird, from the Churchill, Manitoba breeding population (as indicated by the white leg flag) stopped down in Ohio in the fall of 2008. Photo by Steven Jones via eBird.com.
The story of Hudsonian Godwits, as told by Nate, is multi-parted. Hudsonian Godwits breed in three discreet areas. Two of these breeding populations—one in Alaska and another in northern Manitoba—are the subjects of his research. Nate first set out to resolve the migration routes and timing of the two populations, which are discussed here. When he realized that the timing of the Alaskan population was changing, but the Manitoba population was not, he set out to figure out why–this will be the subject of Part II.
Nate and his field techs set out to put geolocators on a number of godwits in each of his two study populations. The difficulty with geolocators is that the birds have to be caught a second time so the data can be downloaded. Fortunately for the researchers, Hudsonian Godwits are faithful to their breeding sites, making it relatively easy to catch the right individuals.
When they did, the findings were remarkable. Like Bar-tailed Godwits, Hudsonians make long non-stop flights both in the spring and fall. But unlike Bar-taileds (more like the recently uncovered route of Great Snipe), southbound hudwits bypass much seemingly suitable habitat, choosing to fly up to seven days without stopping across North America, over (or east of) the Caribbean, not resting until they have reached Argentina (the Churchill population) or (Alaska population) have crossed the northern Andes and reached remote Amazonian Colombia.
Hudsonian Godwits in the Amazon? Nate thought this was entirely unknown, until he talked to Bret Whitney, who said he has seen them in fall in Amazonian Brazil, when river levels are low, feeding on the muddy edges of river islands. This is mind-boggling stuff. And that’s barely half-way to their destination. After fattening up, the godwits depart on another cross-continental non-stop flight to their non-breeding grounds in the Southern Cone of South Ameria. Like their breeding ranges, their non-breeding ranges are also disjunct, with the easternmost (Manitoba) breeding population wintering in Tierra del Fuego and the Alaskan populations wintering on Isla Chiloe off the coast of Chile.
The red flag on this Hudsonian Godwit means that it was banded in Chile. It was photographed there on Isla Chiloe, the main non-breeding grounds of the Alaskan breeding population. Photo by Tom Johnson via eBird.com
Come April, its time for the godwits to return north. If Bar-tailed Godwit is any indication (and it probably is), by the time they depart, they have doubled their body weight before they set off. They need the extra fat, since once they leave they will fly as far north as they can make it in a single flight. Flying up the Pacific Coast, they cross Mexico’s Isthmus of Tehuantepec and usually make it to somewhere between coastal Texas and Nebraska. That’s the goal. But what Nate found is that if the conditions for the 9,000+km flight (about 6,000 miles) are not ideal, they will take a break on the Pacific coast of southern Mexico or northwest Guatemala . It seems, however, that conditions here not prime, as the birds tend to depart within a day or two to continue northward into North America, where a lucky few birders get to see them in their beautiful breeding plumage.
I will pick up the story from here next time, with the final legs of their journey back to their breeding grounds and how this migration and their breeding cycle is being effected by climate change. Stay tuned.Share on Facebook